The present invention relates to cleaner compositions and processes useful for removing scale from metal surfaces. The present invention also relates to cleaner compositions and processes that have reduced base metal loss without inhibiting or significantly inhibiting scale removal from metal surfaces. More particularly, the present invention provides for cleaner compositions and processes for removing magnetite containing scale from metal surfaces, especially in steam generating equipment, and especially high strength metals, such as high strength steels, steels used for pressure to vessel plating, welded metals including welded higher strength steels and welded steels used for pressure vessel plating, steels galvanically coupled to stainless steels, and steels containing heat affected zones resulting from a welding process.
In steam boilers, feed water heaters, piping and heat exchangers where water is circulated and heat transfer occurs, water insoluble salts deposit on the metallic interior surfaces. The nature of the deposits, such as magnetite (Fe3O4) deposits, can vary from a tightly adherent low porosity scale to loosely adherent sludge piles.
Excess scale must be removed periodically to ensure proper functioning of the scale suffering system. Previously, scale removing compositions have been employed. Inorganic acids such as hydrochloric and phosphoric acid as well as organic acids have been used to dissolve iron oxide scale. Alkali metal and amine salts of alkylene polyamine polyacetic acids have also been used to remove iron oxide deposits from ferrous metal surfaces.
Steam generators in pressurized water reactor (PWR) nuclear power plants are heat exchangers transferring heat from a primary coolant (pressurized water) system to a secondary coolant system. In the secondary side of PWR nuclear steam generators, magnetite deposits form over time on both the Inconel(copyright) Alloy 600 and 690 heat transfer surfaces and the mild steel support structures. This causes problems associated with loss of heat transfer efficiency and corrosion of system metallurgies through denting and pitting mechanisms.
These deposits are removed on an infrequent basis using either off-line chemical or mechanical methods. In general, the mechanical methods are less efficient and more costly than the chemical methods. The industry accepted chemical cleaning method utilizes a 10 to 25% diammonium EDTA cleaning solution at a solution pH of 7.5 or higher. The mild-steel corrosion inhibitor employed is an alkylthiopolyimino-amid with a low sulfur content, which is advantageous in that this lessens the stress corrosion cracking of Inconel(copyright) tubes. The cleaning process is typically scheduled to coincide with a refueling outage, and often requires the use of auxiliary heaters to maintain the temperature of the steam generator water at 200xc2x0 F. to 290xc2x0 F.
In U.S. application Ser. No. 09/407,173, filed Sep. 28, 1999, and application Ser. No. 09/245,440, filed Feb. 5, 1999, which are incorporated by reference herein in their entireties, cleaner compositions and methods are disclosed that avoid difficulties inherent in earlier processes. In these applications, compositions are disclosed that will remove iron-containing deposits at lower temperatures than EDTA-based cleaners. These cleaner compositions are disclosed to be less aggressive to the base metal being cleaned and will work at a neutral pH. Additionally, the cleaner compositions that are disclosed do not require halogen ions and have a lower sulfur content, as well as being of lower toxicity and easier to handle. In particular, these applications disclose methods for cleaning iron oxide containing scale from a metal surface, comprising contacting the metal surface with an aqueous composition containing 1-hydroxyethylidene-1,1-diphosphonic acid and at least one of ethoxylated mercaptan and oxidized ethoxylated mercaptan.
There is still a need to provide further improvements in metal oxide dissolution while providing high corrosion inhibition in various environments.
The present invention is directed to a method for cleaning iron oxide containing scale from a surface of at least one of high strength steels, steels used for pressure vessel plating, welded metals, steels galvanically coupled to stainless steels, and steels containing heat affected zones (HAZ) resulting from a welding process, comprising contacting the surface with a composition comprising 1-hydroxy-ethylidene-1,1-diphosphonic acid; at least one of ethoxylated mercaptan and oxidized ethoxylated mercaptan; and at least one third component which in combination with the 1-hydroxy-ethylidene-1,1-diphosphonic acid and at least one of ethoxylated mercaptan and oxidized ethoxylated mercaptan provides a percent corrosion inhibition of greater than about 75% as compared to a composition containing the 1-hydroxy-ethylidene-1,1-diphosphonic acid and the at least one of ethoxylated mercaptan and oxidized ethoxylated mercaptan in the absence of the at least one third component, and a percent oxide dissolution using 80 micron particle sized magnetite of at least about 30% when the solution is maintained at 110xc2x0 F. at pH 6.5 with no agitation and measured at 72 hours.
Moreover, the present invention is directed to a method for cleaning iron oxide containing scale from a surface of at least one of high strength steels, steels used for pressure vessel plating, welded metals, steels galvanically coupled to stainless steels, and steels containing heat affected zones (HAZ) resulting from a welding process, comprising contacting the surface with a composition comprising 1-hydroxy-ethylidene-1,1-diphosphonic acid and at least one of ethoxylated mercaptan and oxidized ethoxytated mercaptan, and at least one of benzotriazole and benzimidazole compound having the following structure: 
wherein X is C or N, each of R1, R2, R3 and R4 is hydrogen, halogen, or a hydrocarbyl group.
The surface can comprise a steel having a carbon content higher than 0.15 wt %, higher than 0.2 wt %, or higher than 0.3 wt %.
The surface comprise can comprise a steel having a Mn content of higher than 0.9 wt %.
The surface can comprise a steel containing up to 0.25 wt % C, 1.15-1.50 wt % Mn, 0.035 wt % P, 0.04 wt % S, 0.21 wt % Si, 0.45-0.60 wt % Mo, and balance Fe. The steel can further contain 0.40-0.60 wt % Ni.
The surface can comprise a steel containing 0.31-0.38 wt % C, 0.60-0.90 wt % Mn, up to 0.04 wt % P, up to 0.05 wt % S, balance Fe.
The surface can comprise a steel containing up to 0.35 wt % C, up to 0.90 wt % Mn, 0.35 wt % P, up to 0.04 wt % S, 0.15-0.30 wt % Si, balance Fe.
The surface can comprise a steel containing at least one of molybdenum, chromium and nickel.
The percent corrosion inhibition can comprise a percent corrosion inhibition of greater than about 80%, more preferably greater than about 85%, and even more preferably greater than about 90%.
The percent oxide dissolution using 80 micron particle sized magnetite, when the solution is maintained at 110xc2x0 F. at pH 6.5 with no agitation and measured at 72 hours, can comprise a percent oxide dissolution of at least about 40%, more preferably at least about 45%, and even more preferably at least about 50%.
The percent corrosion inhibition can comprise a percent corrosion inhibition of greater than about 90%, and the percent oxide dissolution using 80 micron particle sized magnetite, when the solution is maintained at 110xc2x0 F. at pH 6.5 with no agitation and measured at 72 hours, can comprise a percent oxide dissolution of at least about 35%.
Each of R1, R2, R3 and R4 can comprise hydrogen or an alkyl or substituted alkyl, the alkyl or substituted alkyl can contain C1 to C8, more preferably the alkyl or substituted alkyl contains C1 to C6, and even more preferably the alkyl or substituted alkyl contains C1 to C4. The alkyl or substituted alkyl can be branched or straight chained. Three of the R1, R2, R3 and R4 groups can comprise hydrogen, with the fourth R1, R2, R3 and R4 group comprising an alkyl or substituted alkyl group preferably containing C1 to C4.
The benzotriazole compound can comprise butyl-benzotriazole and/or tolyltriazole, and the benzimidazole compound can comprise 5-methyl benzimidazole.
The ethoxylated mercaptan can have the formula:
Hxe2x80x94(xe2x80x94Oxe2x80x94CH2xe2x80x94CH2xe2x80x94)nxe2x80x94Sxe2x80x94R1
wherein R1 is a hydrocarbyl group, n is 1 to 100, and the oxidized ethoxylated mercaptan comprises oxidized derivatives thereof.
Unless otherwise stated, all percentages, parts, ratios, etc., are by weight.
Unless otherwise stated, a reference to a compound or component includes the compound or component by itself, as well as in combination with other compounds or components, such as mixtures of compounds.
Further, when an amount, concentration, or other value or parameter, is given as a list of upper preferable values and lower preferable values, this is to be understood as specifically disclosing all ranges formed from any pair of an upper preferred value and a lower preferred value, regardless whether ranges are separately disclosed.
The present invention relates to methods and compositions for cleaning iron oxide containing deposits from surfaces of at least one of high strength steels; steels used for pressure vessel plating; welded metals including welded high strength steels and welded steels used for pressure vessel plating; steels, including mild steel and high strength steels, galvanically coupled to stainless steels; and steels containing heat affected zones (HAZ) resulting from a welding process, comprising contacting the surfaces with a composition comprising 1-hydroxy-ethylidene-1,1-diphosphonic acid (HEDP) and ethoxylated mercaptan(s) and/or oxidized ethoxylated mercaptan(s), and a third component which in combination with the 1-hydroxy-ethylidene-1,1-diphosphonic acid (HEDP) and ethoxylated mercaptan(s) and/or oxidized ethoxylated mercaptan(s) provides a percent corrosion inhibition of greater than about 75% , more preferably greater than about 80%, even more preferably greater than about 85%, and most preferably greater than about 90%, and a percent oxide dissolution, using 80 micron particle sized magnetite, of at least about 30%, more preferably at least about 40%, even more preferably at least about 45%, and most preferably at least about 50%, when the surfaces are maintained at 110xc2x0 F. at pH 6.5 with no agitation and measured at 72 hours.
It is noted that the determination of percent corrosion inhibition is with respect to a composition containing the same components but in the absence of the third component. Thus, the comparison is made by comparing the corrosion caused by a composition containing 1-hydroxy-ethylidene-1,1-diphosphonic acid (HEDP) and ethoxylated mercaptan(s) and/or oxidized ethoxylated mercaptan(s) in the absence of the third component to the corrosion caused under the same corrosion conditions caused by a composition containing the same concentration of 1-hydroxy-ethylidene-1,1-diphosphonic acid (HEDP) and ethoxylated mercaptan(s) and/or oxidized ethoxylated mercaptan(s) in the presence of the third component.
The present invention also relates to methods and compositions for cleaning iron oxide containing deposits from metal surfaces, especially steels used for pressure vessel plating and higher strength steels which are generally, but not exclusively carbon steels containing more than 0.15 wt %, even as high as more than about 0.2 wt % carbon, and even as high as more than about 0.3 wt % carbon, steels containing more than 0.90 wt % Mn, or steels containing molybdenum, chromium, or nickel as an alloying element, welded metals including welded high strength steels, steels containing heat affected zones (HAZ) resulting from a welding process, and steels, including mild steels and high strength steels galvanically coupled to stainless steels comprising contacting the surfaces with a composition comprising 1-hydroxy-ethylidene-1,1-diphosphonic acid (HEDP) and ethoxylated mercaptan(s) and/or oxidized ethoxylated mercaptan(s), and at least one of benzotriazole and benzimidazole compound(s).
The ethoxylated mercaptan and/or oxidized ethoxylated mercaptan can comprise various ethoxylated mercaptans and/or oxidized ethoxylated mercaptans including those disclosed in application Ser. No. 09/407,173, filed Sep. 28, 1999, which is incorporated by reference herein in its entirety. Thus, the ethoxylated mercaptan preferably has the formula:
Hxe2x80x94(xe2x80x94Oxe2x80x94CH2xe2x80x94CH2xe2x80x94)nxe2x80x94Sxe2x80x94R1
wherein R1 comprises a hydrocarbyl group, and n is 1 to 100, more preferably n is 4 to 20, and even more preferably n is 4 to 12.
As used herein, the term xe2x80x9chydrocarbylxe2x80x9d is understood to include xe2x80x9caliphatic,xe2x80x9d xe2x80x9ccycloaliphatic,xe2x80x9d and xe2x80x9caromatic.xe2x80x9d The hydrocarbyl groups are understood to include alkyl, alkenyl, alkynyl, cycloalkyl, aryl, arylalkyl, and alkaryl groups. Further, xe2x80x9chydrocarbylxe2x80x9d is understood to include branched and unbranched compounds, and both non-substituted hydrocarbyl groups, and substituted hydrocarbyl groups, with the latter referring to the hydrocarbon portion bearing additional substituents, besides carbon and hydrogen.
The number of carbon atoms in R1 can vary. Without wishing to be bound by theory, R1 should have a sufficient number of C atoms to provide activity in the aqueous system to provide corrosion inhibition without significantly inhibiting scale removal. Moreover, the number of C atoms is preferably maintained at an upper limit taking at least into consideration compound expense and/or the ability of the compound to be maintained in a useful state in the aqueous system, such as ensuring sufficient solubility of the compound in the aqueous system. Preferably, the hydrocarbyl group contains less than 30 carbon atoms.
Preferably, R1 is an alkyl or substituted alkyl, preferably containing C1 to C30, more preferably C6 to C18, and even more preferably C8 to C14, which can be branched or straight chain, and the substitutions can preferably include hydroxy, sulfonate, phosphate, amino and aromatic groups.
In general, ethoxylated mercaptans can be prepared from a reaction of ethylene oxide and mercaptan of the form R1SH, wherein R1 is defined as above. Examples of R1SH include, but are not limited to, benzyl mercaptan, cyclohexyl mercaptan, dipentene dimercaptan, ethyl mercaptan, ethylcyclohexyl dimercaptan, ethylthioethanol, isopropyl mercaptan, n-butyl mercaptan, n-decyl mercaptan, n-dodecyl mercaptan, n-hexyl mercaptan, n-octyl mercaptan, n-propyl mercaptan, pinanyl mercaptan-2, s-butyl mercaptan, t-butyl mercaptan, t-dodecyl mercaptan (such as Sulfole(copyright)120 available from Phillips Specialty Chemicals, Bartelsville, Okla.), t-mix mercaptan (such as Sulfole(copyright)100 available from Phillips Specialty Chemicals, Bartelsville, Okla.), t-nonyl mercaptan (such as Sulfole(copyright)90 available from Phillips Specialty Chemicals, Bartelsville, Okla.), 1,2 ethanedithiol, 2-ethylhexyl-3-mercaptopropionate, 2-mercaptoethanol, and 3-mercapto-1-propanol.
Preferably, the ethoxylated mercaptan includes, but is not limited to, ethoxylated alkyl mercaptans, most preferably ethoxylated alkyl mercaptans having about 4 to 12 moles of ethoxylation per mole of mercaptan, including ethoxylated tertiary dodecyl mercaptans, such as those having 6 moles of ethoxylation per mole of mercaptan, e.g., ALCODET 260 available from Shibley Chemicals, Elyria, Ohio, and manufactured by Rhone-Poulenc, those having 8 moles of ethoxylation per mole of mercaptan, e.g., ALCODET SK available from Shibley Chemicals, Elyria, Ohio, and manufactured by Rhone-Poulenc, and those having 10 moles of ethoxylation per mole of mercaptan, e.g., ALCODET 218 available from Shibley Chemicals, Elyria, Ohio, and manufactured by Rhone-Poulenc; and ethoxylated n-dodecylmercaptan, such as those having about 4.9 or about 8.2 moles ethoxylation per mole of mercaptan. Burco TME, which is available from Burlington Chemicals, Burlington, N.C., is a particularly preferred ethoxylated alkyl mercaptan. Ethoxylated 2-phenylethyl mercaptans having about 6.7 moles ethoxylation per mole of mercaptan are also preferred.
Preferably, oxidized ethoxylated mercaptans are utilized in the composition according to the present invention. In particular, it noted that oxidized ethoxylated mercaptans provide exceptional corrosion inhibition without inhibiting scale removal from metal surfaces. Thus, while ethoxylated mercaptans have been found to provide exceptional corrosion inhibition combined with very low levels of metal loss when utilized in conjunction with HEDP, it was further discovered that oxidized ethoxylated mercaptans provide an even greater corrosion inhibition when utilized in conjunction with HEDP.
The ethoxylated mercaptan can be oxidized utilizing various procedures, and one having ordinary skill in the art would be able to oxidize ethoxylated mercaptans following the guidance provided herein. For example, methods such as disclosed in xe2x80x9cAdvanced Organic Chemistryxe2x80x9d by Jerry March, 3rd Edition, pages 1089-1090, 1985, published by John Wiley and Sons, which is incorporated by reference in its entirety.
For example, without limiting the manner of oxidizing the ethoxylated mercaptans, the ethoxylated mercaptans can be oxidized using hydrogen peroxide. Thus, as an example of oxidization of ethoxylated mercaptans according to the present invention, the ethoxylated mercaptans can be reacted with hydrogen peroxide, such as by utilizing an aqueous solution of hydrogen peroxide preferably containing about 1 to 70 wt %, more preferably about 30 to 50 wt %, at a temperature of preferably about 25xc2x0 C. to 100xc2x0 C., more preferably about 40xc2x0 C. to 60xc2x0 C., for a sufficient period of time to oxidize the ethoxylated mercaptan, preferably about 30 minutes to 8 hours, more preferably about 1 to 2 hours.
Residual hydrogen peroxide can be removed utilizing any method for removing the hydrogen peroxide which is not detrimental or which is substantially non-detrimental to the oxidized ethoxylated mercaptan. For example, residual hydrogen peroxide can be removed by raising the pH of the reaction composition that contains the oxidized ethoxylated mercaptan and the residual hydrogen peroxide, or a catalyst for hydrogen peroxide can be added to reaction composition. Thus, for example, the pH of the reaction composition can be raised to at least about 10 and/or a catalyst, such as at least one of platinum, palladium, ferric chloride, cobalt chloride, and cupric chloride can be added to the reaction composition. While there is no upper limit to the pH, preferably the pH is maintained below about 14, with a preferred range being about 10-12.
Without wishing to be bound by theory, it is believed that the sulfur component of the ethoxylated mercaptan is oxidized in the oxidation reaction to sulfoxide. Moreover, it is believed that at least some of the sulfoxide is further oxidized to sulfone. Thus, it is believed that the oxidized ethoxylated mercaptan contains sulfoxide and/or sulfone groups.
For purposes of the present invention, the term ethoxylated mercaptan can include a mixture of one or more ethoxylated mercaptans, and the term oxidized ethoxylated mercaptan (also alternatively referred to herein as xe2x80x9cderivatives of ethoxylated mercaptansxe2x80x9d) can include mixtures of one or more oxidized ethoxylated mercaptans. Moreover, according to the present invention, there can be mixtures of ethoxylated mercaptans and oxidized ethoxylated mercaptans.
Benzotriazole and benzimidazole compounds according to the present invention can comprise compounds of the following structure: 
wherein X can be C or N, each of R1, R2, R3 and R4 can comprise hydrogen, halogen, e.g., chlorine, bromine and/or iodine, or a hydrocarbyl group. Preferably, R1, R2, R3 and R4 comprise hydrogen, chlorine or an alkyl or substituted alkyl, preferably containing C1 to C8, more preferably C1 to C6, and even more preferably C1 to C4, which can be branched or straight chain, and the substitutions can preferably include hydroxy, sulfonate, phosphate, amino and aromatic groups. Most preferably, three of the R1, R2, R3 and R4 groups comprise hydrogen, and the fourth R1, R2, R3 and R4 group comprises an alkyl group containing C1 to C8, more preferably C1 to C6, and even more preferably C1 to C4. Still more preferably, R1, R3 and R4 are hydrogen, and R2 comprises from C1 to C6 carbon atoms, more preferably from C1 to C4 atoms. Preferred benzotriazole compounds include benzotriazole, butyl-benzotriazole (wherein R2 is a butyl group), and tolyltriazole (wherein R2 is a methyl group). Tolyltriazole is also known by its Chemical Abstract No. as CAS#29385-43-1, and synonyms include tolutriazole, methyl-1H-benzotriazole, 5-methylbenzotriazole, 5-methyl-1,2,3-benzotriazole and cobratec tt-100.
Preferred benzotriazole compounds include:
5-chloro benzotriazole
5,6 dimethyl benzotriazole
tolyltriazole (CAS#29385-43-1)
benzotriazole (CAS#95-14-7)
butyl benzotriazole
ethyl benzotriazole
diethyl benzotriazole
Preferred benzimidazole compounds include:
Benzimidazole [51-17-2] Aldrich Chemical, Milwaukee, Wis.
5-Methyl benzimidazole [614-97-1] Aldrich Chemical, Milwaukee, Wis.
2-Methylbenzimidazole [615-15-6] Aldrich Chemical, Milwaukee, Wis.
The metal can be any metal for which removal of an iron oxide while obtaining corrosion inhibition is desired. In particular, metals treated according to the present invention can include, but are not limited to, mild steel, high-strength low-alloy steel (HSLA), steels used for pressure vessel plating, and high strength steels which are generally, but not exclusively carbon steels containing more than 0.15 wt % carbon, even as high as more than 0.2 wt % carbon, and even has high as more than 0.3 wt % carbon, steels containing more than 0.90 wt % Mn, or steels containing molybdenum, chromium, or nickel as an alloying element. Preferably, metals treated according to the present invention include steels used for pressure vessel plating, high strength steels, welded metals including welded high strength steels, steels containing heat affected zones (HAZ) resulting from a welding process and steels, including mild steel and high strength steel galvanically coupled to stainless steel, such as Inconel(copyright) Alloy 600 (UNS N06600) or Inconel(copyright) Alloy 690 stainless steel (UNS N06690).
For example, high strength steels and steels used for pressure vessel plating according to the present invention include SA-533 grade A (UNS K12521); SA-533 grade B (UNS K12539); AISI-1035 (UNS G10350); and SA-515 Grade 70 (UNS K03101). SA-533 grade A (UNS K12521) is a high tensile strength, low carbon steel that contains up to 0.25 wt % C, 1.15-1.50 wt % Mn, 0.035 wt % P, 0.04 wt % S, 0.21 wt % Si, 0.45-0.60 wt % Mo, and balance Fe, and is generally used for pressure vessel plating. SA-533 grade B (UNS K12539) and SA-515 Grade 70 (UNS K03101) are similar in nature to SA-533 grade A (UNS K12521). SA-533 grade B contains 0.40-0.60 wt % Ni in addition to the components of SA-533 grade A. AISI-1035 contains 0.31-0.38 wt % C, 0.60-0.90 wt % Mn, up to 0.04 wt % P, up to 0.05 wt % S, balance Fe. SA-515 grade 70 contains up to 0.35 wt % C, up to 0.90 wt % Mn, 0.35 wt % P, up to 0.04 wt % S, 0.15-0.30 wt % Si, balance Fe.
Expanding upon the discussion of welded metals and heat affected zones, reference is made to Metallurgy, by B. J. Moniz, American Technical Publishers, Inc., Homewood, Ill. 60430, 1994, pages 422-423, which is incorporated by reference in its entirety herein. Thus, it is noted that a weld joint includes three distinct metallurgical regions, which are the weld bead (which includes the weld metal), the heat affect zone (which is a narrow region of the base metal adjacent to the weld bead, which is metallurgically altered during the heat of welding), and the base metal (which is the region of metal that is joined by the welding process and is not metallurgically affected by the heat of welding).
The cleaning composition of the present invention is typically added to steam generating systems, beat exchangers and other high pressure vessels where heat transfer to an aqueous medium occurs. These systems often have ferrous metal surfaces where magnetite scaling can occur.
The cleaning composition is preferably employed in the secondary side of Pressurized Water Reactor nuclear steam generators which contain bundles of metal tubes held in place by tube sheets and support plates.
The cleaning composition may be added to systems, such as the above-noted systems, as an active recirculating system, e.g., where the system is undergoing operation to at least partially, and preferably substantially completely or completely achieve usual system performance such as by being on-line. The cleaning composition may also be preferably added off-line, such as adding the cleaning composition to an off-line nuclear steam generator. Off-line addition includes static cleaning wherein the cleaning composition is not moving or substantially non-moving, such as wherein the cleaning composition is added to a container and/or a pipe and not circulated therein. Moreover, off-line addition includes scale removal wherein the cleaning composition is caused to flow, such as by being agitated, such as by bubbling with an inert gas, such as nitrogen, or by being circulated, such as by a pump and/or gravity. When added off-line, the cleaning composition may be left in contact with the metal surface for extended periods of time, such as long as 7 days, even as long as 10 days, or longer. This period of time will vary depending upon the temperature of the water and the extent and amount of magnetite scale on the surfaces contained therein. In particular, the lower the temperature, the longer the contact time required to removal the scale. For example, at temperatures of about 25xc2x0 C. to 100xc2x0 C., in a static cleaning system, the cleaning composition can be contacted with the surface to be cleaned for about 3 hours to 10 days.
The cleaning composition may be employed alone or as a precursor to the use of mechanical cleaning methods such as sludge lancing, upper bundle hydraulic cleaning, ultrasonic technology, or any technique that is intended to remove oxide sludge by physical means.
Typically, the cleaning composition is added as an aqueous solution. The individual components of the composition may be added separately or together depending upon the particular system treated. Additionally, the cleaning composition may be added neat to the system to be treated. The total amount of cleaning composition to be added to the system will vary depending upon the amount of magnetite scale and the temperature of the water. The cleaning composition may be added to the system to be treated in an amount ranging from about 0.1 to about 50,000 parts ethoxylated mercaptan per million parts of solution in the system, more preferably about 0.1 to about 20,000 parts ethoxylated mercaptan per million parts of solution in the system, more preferably from about 500 to 10,000 parts ethoxylated mercaptan per million part of solution in the system, even more preferably from about 1,000 to 5,000 parts ethoxylated mercaptan per million parts of solution in the system, with one preferred value being about 2,500 parts ethoxylated mercaptan per million parts of solution in the system. Moreover, the cleaning composition may be added to the system to be treated in an amount ranging from about 1 to 200,000 parts HEDP per million parts of solution in the system, preferably 5,000 to 100,000 parts HEDP per million parts of solution in the system, even more preferably 20,000 to 80,000 parts HEDP per million parts of solution in the system, with one preferred value being about 43,500 parts HEDP per million parts of solution in the system. Still further, the cleaning composition may be added to the system to be treated in an amount ranging from about 0.1 to about 50,000 parts benzotriazole and/or benzimidazole compound per million parts of solution in the system, more preferably about 0.1 to about 20,000 parts benzotriazole and/or benzimidazole compound per million parts of solution in the system, more preferably from about 500 to 10,000 parts benzotriazole and/or benzimidazole compound per million parts of solution in the system, even more preferably from about 1,000 to 5,000 parts benzotriazole and/or benzimidazole compound per million parts of solution in the system, with one preferred value being about 2,500 parts ethoxylated mercaptan per million parts of solution in the system.
The weight ratio of HEDP to at least one of ethoxylated mercaptan and oxidized ethoxylated mercaptan will range from about 4 to 1 to 200 to 1, more preferably from about 4 to 1 to 80 to 1, even more preferably from about 4 to 1 to 50 to 1, with one preferred weight ratio being about 17 to 1.
The weight ratio of HEDP to at least one of benzotriazole and benzimidazole compounds will range from about 4 to 1 to 200 to 1, more preferably from about 4 to 1 to 80 to 1, even more preferably from about 4 to 1 to 50 to 1, with one preferred weight ratio being about 17 to 1.
The inventive cleaning composition may be added to the system to be treated with additional chemicals serving other purposes in the system. This holds true whether the chemical is added with the cleaning solution or is already present in the aqueous system.
These other chemicals typically can be reducing agents such as L-ascorbic acid, hydroquinone, sodium sulfite, diethylhydroxylamine, hydrazine, erythorbic acid or carbohydrazide; anionic polymers such as carboxylates (e.g. polyacrylic acid, polymethacrylic acid and copolymers thereof) poly(alkenyl)phosphonic acids; surfactants such as phosphate esters, polyethylene oxide, polypropylene oxide and copolymers thereof, fatty acid amides and ethoxylated alcohols; hydrotropes such as sodium xylene sulfonate; and corrosion inhibitors in addition to benzotriazoles and tolyltriazole, which are known copper corrosion inhibitors. For purposes of the present invention, this list is merely representative and not meant to be exclusive.
Moreover, it is once again noted, as indicated above, that the compositions and processes of the present invention can include other corrosion inhibitors in addition to the ethoxylated mercaptan and/or oxidized ethoxylated mercaptans and the benzimidazole and benzotriazole compounds of the present invention.
The cleaning composition of the present invention can be employed at pH""s at least about 5 or above, more preferably at least about 6 or above, with a preferred range of about 5 to 12, more preferably about 6 to 12, and even more preferably about 6 to 8. The pH of the cleaner composition can be adjusted, preferably to a pH greater than about 5, more preferably to a pH greater than about 6, and more preferably to a pH of about 6 to 8, using various materials that can raise the pH of the system, preferably by using alkali metal hydroxide salts such as NaOH or KOH, organic amines, or ammonia.
Besides the ability to remove magnetite deposits from ferrous metal surfaces, particularly the secondary side of PWR nuclear steam generators, the present inventors anticipate that the cleaning composition will be effective in pre-operational boiler cleaning in fossil fuel systems, off-line and on-line boiler cleaning, cleaning of closed and open loop cooling systems and heat exchangers. Moreover, the present invention can be utilized in any system requiring the removal of magnetite from high strength steels.